There is as much as 4psi difference between cold tire and warmed up tire. Hence you always have to mesure at cold.
TMPS causes more troubles for drivers as well as Subaru Dealers. Another reason why government shouldn't get into the business of how to design cars. This is one system I can happily live without. People that care about their cars know to check tire pressure regularly and not to overload the tires like those Ford Explorer drivers. Why treate everybody like those dumies.